Mainly conducting research on the comprehensive utilization of photovoltaic and thermal energy in dispersed solar energy, analyzing the characteristics of solar energy dispersion, seasonality, etc., proposing and designing a thermal energy storage system on a thermal island to compensate for heat loss, in order to obtain a stable energy supply; Develop a dual axis tracking system that can accurately track sunlight, effectively improve photoelectric conversion efficiency, and ultimately propose an efficient and reliable photovoltaic thermal comprehensive utilization system.
The system service designed is aimed at rural users, and the design purpose of this article is to ensure that the thermal power supply can meet basic living needs, with low cost and high reliability.
There are currently two forms of solar energy for household use: flat panel solar collectors and vacuum tube solar collectors, which can generally only produce low-temperature hot water; and direct solar power generation systems. Although both are fixed devices, they cannot be integrated due to the different ways of collecting sunlight. These two forms of systems, although inexpensive, have low photothermal and photoelectric efficiency. Therefore, it cannot be used as a reference model. At the same time, it is necessary to draw on the common problems of these two forms of solar energy devices as the problems to be avoided or solved in this article’s design.
In the centralized solar energy system, the high magnification concentrated photovoltaic thermal comprehensive utilization system has developed relatively maturely in recent years, mainly used for centralized power generation, community heating, or places with higher heating demand. Due to its high power concentration, the heat generated by its photovoltaic cells is much higher than that of non concentrated solar panels. Therefore, high power concentrated solar energy systems adopt active cooling methods for cooling. Generally, circulating water cooling is used as the active cooling method, and the hot water is then transmitted to other media or domestic water through the overheat exchange plate to achieve the goal of cogeneration.
The high magnification concentrated photovoltaic thermal comprehensive utilization system includes: concentrator, reflection system, solar tracking system, water cooling system, thermal storage system, and power generation grid connection system. According to the design purpose of this article, combined with the needs of the service objects of household solar photovoltaic thermal comprehensive utilization system, the following design ideas are obtained by analyzing the above system:
- Reducing system structure can improve system reliability, reduce maintenance costs, and lower system costs;
- Lower the system design standards to meet user needs.
Through theoretical calculations and various attempts, the following methods are adopted to achieve the above design concept:
- Reduce the spotlight multiple and optimize the spotlight. The Fresnel lens used in high magnification solar energy systems is too expensive, so homemade lenses are used instead of Fresnel lenses and low magnification focusing is adopted. This low magnification focusing method avoids the limitation that high magnification concentrating solar energy systems can only be applied in areas with a high proportion of direct radiation to total radiation.
- Abandoning the reflection system and switching to a transmissive focusing method may result in half wave loss when sunlight passes through the lens. However, for the service object of this article, its power generation and heat generation should be able to meet user needs.
- Replace the heat storage of high magnification solar energy systems with more economical and practical surface soil heat storage methods, as long as they can meet the user’s daily heat needs, including winter heating needs.
- When there is surplus power connected to the grid, the inverter made by modifying the low-cost DC motor can achieve surplus power connected to the grid.
In rural China, a typical homestead covers an area of 200 square meters, with a building area of 70 square meters, 6 people per household, and a monthly electricity consumption of 400 kWh. The design goal of this system is to install solar thermal panels on a roof area of 40 square meters for rural households, with an annual electricity production of no less than 5000 kWh, and to meet the normal heating needs of daily life, including winter heating needs.